Showing papers on "Epimer published in 2010"
TL;DR: The final deprotection of which successfully afforded (-)-MRY D2 and epi-MRy D2 (53) after HPLC separation of the diastereomers would afford ready access to a range of analogues simply by altering each component.
Abstract: Full details of the first total synthesis of (−)-muraymycin (MRY) D2 and its epimer, the antibacterial nucleoside natural product, are described. Key strategic elements of the approach include the preparation of the urea dipeptide moiety found in the muraymycins containing an l-epi-capreomycidine via a nitrene C−H insertion of the sulfamate 10 and the fully protected muraymycin skeleton at a late stage by an Ugi four-component reaction. Thus, the nitrene C−H insertion of the sulfamate 10 with 10 mol % of Rh2(esp)2 catalyst gave the cyclic sulfamates 11a and 11b in 47% yield (11a:11b = 1:2.0). Construction of the cyclic guanidine skeleton was effected through the HgBr2-promoted cyclization of 42 followed by desulfonylation upon acetolysis of the oxathiazinane ring to give 43 in good yield. The amine obtained by selective removal of the Cbz group of the alcohol 44 was reacted with MeSC(═O)-l-Val-O-t-Bu (38) to provide 45, which was oxidized to the carboxylic acid 46. Reaction of 46, isonitrile 51, isovalera...
76 citations
TL;DR: X-ray crystal analysis for D-psicose (C3position epimer of D-fructose) crystallized from aqueous solution was successfully performed for the first time as mentioned in this paper.
Abstract: X-ray crystal analysis for D-psicose (C3-position epimer of D-fructose) crystallized from aqueous solution was successfully performed for the first time. It was confirmed that D-psicose crystallize...
57 citations
TL;DR: (+)-Steviamine, the enantiomer of the natural (-)-steviamine and its corresponding C5 epimer have been synthesized from the D-ribose-derived cyclic nitrone.
49 citations
TL;DR: The first synthesis of the marine endoperoxide 9,10-dihydroplakortin, of its C10-desethyl analogue, and of their corresponding C6 epimers is described, which features a one-pot three-step hydroperoxysilylation/cyclization reaction for the construction of the end operoxide ring system.
Abstract: The first synthesis of the marine endoperoxide 9,10-dihydroplakortin, of its C10-desethyl analogue, and of their corresponding C6 epimers is described. Stereogenic centers at C4 and at the lateral chain have been stereoselectively synthesized through Evans' chiral auxiliary chemistry. Moreover, the reported synthesis features a one-pot three-step hydroperoxysilylation/cyclization reaction for the construction of the endoperoxide ring system. Homologation of the aldehyde resulting from diol cleavage through a Wittig-based strategy gave access to the ester-containing lateral chain at C3.
43 citations
TL;DR: Three new metabolites having a spiro-heterocyclic gamma-lactam core, cephalimysins B-D (1-3), as well as FD-838 (4) were isolated from a culture broth of Aspergillus fumigatus that was originally separated from the marine fish Mugil cEPhalus.
Abstract: Three new metabolites having a spiro-heterocyclic gamma-lactam core, cephalimysins B-D (1-3), as well as FD-838 (4) were isolated from a culture broth of Aspergillus fumigatus that was originally separated from the marine fish Mugil cephalus. Compounds 1-3 are the diastereomers of 4. Compounds 2 and 3 exhibit an opposite absolute configuration at a spiro carbon to that of other known naturally occurring spiro-heterocyclic gamma-lactams. In addition, we succeeded in the chemical transformation of the four natural products (1-4) into their epimers (1'-4') at C-8 to afford all the stereoisomers of FD-838 (4) with three stereogenic centers. Consequently, the relationship between the absolute configuration at stereogenic centers and the CD Cotton effects for these compounds could be unambiguously established. All of the compounds except 1 moderately inhibited the growth of cultured P388 and HL-60 cell lines.
40 citations
TL;DR: The total synthesis of the potent antifungal and antibiotic cyclic depsipeptide LI-F04a and its side chain epimer was accomplished using macrolactonization to assemble the cyclic peptide core, followed by attachment of the 15-guanidino-3-hydroxypentadecanoyl (GHPD) side chain.
25 citations
TL;DR: The novel, simple synthesis of N-Bz-protected D-daunosamine and D-ristosamine from these oxazolines is described in this paper.
25 citations
TL;DR: In this article, an efficient stereoselective synthesis of dendrobate alkaloid (+)-241D and its C-4 epimer was achieved from the inexpensive, commercially available starting material decanal (10) in an overall yield of 21.9% and 21.1%, respectively.
24 citations
TL;DR: A simple and highly efficient synthetic route has been developed for synthesis of (R)-rugulactone (1a) and its 4S epimer 1c by employing proline-catalyzed alpha-aminooxylation, Sharpless epoxidation, Mitsunobu reaction as chirality introuducing steps.
23 citations
TL;DR: A short and stereoselective synthesis of (−)-codonopsinol 5 and its C-2 epimer 6 were accomplished from commercially available starting material d -1,5-gluconolactone, using acid mediated amido cyclisation as the key step.
20 citations
TL;DR: Evaluated precursor structures obtained by various enzymatic procedures could be used for glycosylations employing triflic acid/N-iodosuccinimide to give the corresponding human milk pentasaccharides in good yields.
Abstract: α,2-3- and α,2-6-sialylated lactosaminide precursor structures obtained by various enzymatic procedures could be used for glycosylations employing triflic acid/N-iodosuccinimide. Easily accessible selectively protected lactoside derivatives served as acceptor disaccharides to give the corresponding human milk pentasaccharides in good yields. These were characterized by spectroscopic means in the form of their peracetylated derivatives.
TL;DR: The proposed structure of the benzolactone queenslandon ( 6 ) was synthesized utilizing a triol containing building block prepared from d -ribose as discussed by the authors. But this method did not lead to the macrocycle.
TL;DR: The conformational analysis and the glycosidase inhibitory properties of all the new C-3 substituted azafagomines synthesized are reported and those having L-fuco configuration have shown a selective inhibition of α-L-fucosidases.
TL;DR: The first total synthesis of (3R), (5R)-5-hydroxy-de-Omethyllasiodiplodin and its epimer was reported from malic acid as mentioned in this paper.
TL;DR: The novel concise synthesis of 3-Hydroxy- l -arginine presented here allows the efficient preparation of both 3-epimers of this β-hydroxy amino acid and offers the potential to obtain suitably isotope-labelled derivatives for the elucidation of epicapreomycidine assembly in the biosynthesis of complex natural products.
TL;DR: The synthesis of the natural compound (8S *, 14S * )-8-(4'-hydroxybenzyl)-2,3-dimethoxyberbin-10-ol and its C-8 epimer has been conveniently developed by making use of the diastereoselective Stevens rearrangement of the corresponding N-(arylmethyl)berbinium salts as the key step as mentioned in this paper.
TL;DR: The first doubly labeled synthesis of [2-13C, 4-13c]-(2R, 3S)-catechin was described in this paper. But the synthesis of doubly labelled catechines is not a new problem.
Abstract: The first synthesis of doubly labeled, [2-13C, 4-13C]-(2R,3S)-catechin 15 and [2-13C, 4-13C]-(2R,3R)-epicatechin 18 starting from labeled 2-hydroxy-4, 6-bis(benzyloxy)acetophenone 3 and labeled 3, 4-bis(benzyloxy)-benzaldehyde 7 are described. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: Preussin (1) and its 5-epimer were synthesized from the divinylcarbinol (3) with Sharpless asymmetric epoxidation of 3 and the oxidative cyclization of 9 with PDC as the key steps.
Abstract: (+)-Preussin (1) and its 5-epimer were synthesized from the divinylcarbinol (3) with Sharpless asymmetric epoxidation of 3 and the oxidative cyclization of 9 with PDC as the key steps.
TL;DR: In this article, the use of the (S)-α-methylbenzyl group as a chiral auxiliary has allowed the diastereoselective ortho-deprotonation of a chromium tricarbonyl complexed phenoxy ring.
TL;DR: Comparison of physical properties of these epimer pairs shows that at least qualitative effects can be correlated with the configuration at C-20 of epimer 20-amino steroids.
Abstract: Conanine (IIh) and heteroconanine (IIIh) were obtained as the ultimate products of two reaction sequences starting from 3β-hydroxy-Sα.-pregnan-20-one oxime and involving the preparation of epimeric 20-amino steroids.
Comparison of physical properties of these epimer pairs shows that at least qualitative effects can be correlated with the configuration at C-20 of epimer 20-amino steroids.
TL;DR: The structure-activity relationships for the cytoprotective activity against cytotoxicity induced by 3-morpholinosydnonimine (SIN-1) in nerve growth factor (NGF)-differentiated PC12 cells was examined and the C-8/C-9 double bond, but not the stereogenic center derived from alanine, was found to play a key role in the cytopsized activity.
Abstract: We developed an efficient, stereoselective synthetic method for the diketopiperazine moiety of neoechinulin A and its derivatives. The intramolecular cyclization at 80 oC proceeded with minimal racemization of the stereogenic center at C-12 on neoechinulin A, even though the cyclization at 110 oC caused partial racemization. In contrast with these results, the cyclization on diketopiperazine of 8,9-dihydroneoechinulin A derivatives did not cause epimerization of the stereogenic centers, even at 110 °C. We examined the structure-activity relationships for the cytoprotective activity against cytotoxicity induced by 3-morpholinosydnonimine (SIN-1) in nerve growth factor (NGF)-differentiated PC12 cells. The C-8/C-9 double bond, but not the stereogenic center derived from alanine, was found to play a key role in the cytoprotective activity.
TL;DR: 8-Epitacrolimus, a new l-pipecolic acid macrolide lactone, was obtained by base-catalyzed epimerization of tac-506, an important immunosuppressive drug, and its structure determined by a single-crystal X-ray diffraction method.
Abstract: 8-Epitacrolimus (2), a new l-pipecolic acid macrolide lactone, was obtained by base-catalyzed epimerization of tacrolimus (FK-506, 1), an important immunosuppressive drug, and its structure determined by a single-crystal X-ray diffraction method. The compound was fully characterized by spectroscopic techniques. The epimer is of importance due to its potential biological effects as well as because of its possible formation during formulation, handling, and use of tacrolimus products.
TL;DR: In this paper, the conformational energy of a ψ-axial 2-t-butyl group was estimated at 8.6±1.3 kJ mol−1.
Abstract: Chemical equilibration of epimeric 2-t-butyl-5-methyl-1, 3-oxathiolans led to -ΔHo=4.60±0.05 kJ mol−1 and -ΔSo=2.9±0.16 J mol−1K−1 for the trans cis equilibrium. From them and the values of 1H vicinal coupling constants the conformational energy of a ψ-axial 2-t-butyl group was estimated at 8.6±1.3 kJ mol−1. A microcalorimetric determination of the enthalpy difference for the epimer equilibrium resulted in a less accurate value of 4.5±1.0 kJ mol−1 and pointed out some disadvantages connected with the latter method.
TL;DR: The title ketone 1 afforded > 95% of fairly stable t-1,3,3-trichloro-t-2methoxy-4,6,6-trimethyl-1-2-epoxycyclohexane (2) by reaction with cold methanolic sodium methoxide.
Abstract: The title ketone 1 afforded > 95% of fairly stable t-1,3,3-trichloro-t-2-methoxy-4,6,6-trimethyl-1,2-epoxycyclohexane (2) by reaction with cold methanolic sodium methoxide. Heating or contact with sulfuric acid or boron trifluoride caused stereospecific rearrangement of 2 into t-2,3,3-trichloro-2-methoxy-4,6,6-trimethylcyclohexanone (3). On the contrary, rearrangement into the epimeric ketone 4 was induced by trifluoroacetic or dichloroacetic acid in carbon tetrachloride. Epimer 4 was distinctly more reactive than 3 towards dehalogenation with zinc in acetic acid and towards sodium methoxide. Good yields of 3,3-dichloro-4, 6,6-trimethyl-1,2-cyclohexanedione (7) were obtained from 2, 3 or 4 in hot solutions of zinc chloride in acetic acid.
The symmetric 2,2,6,6-tetrachloro-3,3,5,5-tetramethylcyclohexanone (8) showed analogous reactions.
TL;DR: A short synthesis of hydroxyethylene dipeptide isostere, a core unit of the HIV-protease inhibitors ritonavir and lopinavir, its C-3 epimer and C 2 symmetric diamino diol is described in this article.
Abstract: A short synthesis of hydroxyethylene dipeptide isostere, a core unit of the HIV-protease inhibitors ritonavir and lopinavir, its C-3 epimer and C 2 symmetric diamino diol is described The crucial aspects of the synthesis are self-cross metathesis and exploitation of C 2 -symmetric of the metathesis product 8 to obtain the required skeleton
TL;DR: The synthesis of the C2 and C3 epimer and also the enantiomer of jaspine B from D-glucose is reported and the cytotoxicity of these isomers along with jaspines B and its C2 epimer on MCF7 cells has been correlated with commercially available anticancer drug Epirubicin.
Abstract: The synthesis of the C2 and C3 epimer and also the enantiomer of jaspine B from D-glucose is reported. The cytotoxicity of these isomers along withjaspine B and its C2 epimer on MCF7 cells has been correlated with commercially available anticancer drug Epirubicin.
TL;DR: In this article, the 6α-methyl-3-oxo-Δ4 compounds in the estrene and 19-nor-pregnene series have been converted to their 3-desoxo derivatives.
Abstract: The dehydration-epimerization reaction applied to a 5α-hydroxy-6β-methyl-3-oxo-19-nor-steroid, under acid conditions, leads to a mixture of the 6α-methyl-3-oxo-Δ4-19-nor-steroid and its 6β-epimer. This is in contrast to the normal steroid series, in which exclusively the 6α-methyl epimer is formed. A complete conversion to the 6α-methyl compounds can be achieved by alkaline hydrolysis of the corresponding 3-acetoxy-6-methyl-Δ3,5 compounds.
Several 6-methyl-3-oxo-Δ4 compounds in the estrene and 19-nor-pregnene series have been converted to their 3-desoxo derivatives.
TL;DR: In this paper, the synthesis of two epimeric tripeptides δ-( l -α-aminoadipoyl)- l -cysteinyl- d -(O-methyl)- d -threonine (13) and δ( l −α-amino-drug-polygonal-polymorphic-polyethylene (α-AMPDP) (14), modified substrates for the isopenicillin-N synthase enzyme were described.
Abstract: The paper describes the synthesis of two epimeric tripeptides δ-( l -α-aminoadipoyl)- l -cysteinyl- d -(O-methyl)- d -threonine (13) and δ-( l -α-aminoadipoyl)- l -cysteinyl- d -(O-methyl)- d -allothreonine (14), modified substrates for the isopenicillin-N synthase enzyme. The d -allothreonine tripeptide (14) has been shown to be an excellent substrate for the enzyme whereas the d -threonine epimer did not react at all. The compound formed by the enzyme with the d -allothreonine tripeptide is a new 2-α-methoxypenicillin.
TL;DR: The Pschorr reaction performed under non-classical reaction conditions on the diazonium chloride derived from 2-amino-N-methyl-N-(3methyl-1-phenyl-1H-pyrazol-5-yl)benzamide 1 afforded the epimers (3′R,4′S)- and (3´R, 4´R)-4′-chloro-2´,4´-dihydro-2,5´-dimethyl-2′-phenYLspiro[isoindoline
Abstract: The Pschorr reaction performed under non-classical reaction conditions on the diazonium chloride derived from 2-amino-N-methyl-N-(3-methyl-1-phenyl-1H-pyrazol-5-yl)benzamide 1 afforded the epimers (3′R,4′S)- and (3′R,4′R)-4′-chloro-2′,4′-dihydro-2,5′-dimethyl-2′-phenylspiro[isoindoline1,3′-3′H-pyrazol]-3-one 4a and 4b together with the related enantiomers. The epimers were easily converted under acid conditions into both 4-chloro-3-methyl-5-[2-(methylcarbamoyl)phenyl]-1-phenyl-1H-pyrazole 5 and the potentially pharmacologically active 3-methyl-1-phenyl-1H-[2]benzopyrano[4,3-c]pyrazol-5-one 3, whereas under base conditions, as well as thermally, only compound 5 was obtained.The molecular structure of epimer 4a and that of the derivative 5 were confirmed by single-crystal X-ray analysis. The crystal of compound 5 is characterized by the presence of two conformational isomers in the unit cell.